“The Effects of Impacts on Planetary Climates: From Dead Dinosaurs on Earth to the River Valleys on Mars,” Brian Toon, University of Colorado, 4 p.m., 22 Deike Building, Department of Geosciences (814-865-2622).

"Nanoparticle Mass Spectrometry: How it Works and What It Tells Us About Atmospheric Processes," Murray Johnston, University of Delaware, 2:30 p.m., 102 Chemistry Building, host: Miriam Freedman, Chemistry Department (814-865-4543).